1. Field of the Invention
This invention relates to a system for transmitting digital data with low cross talk.
2. Description of the Prior Art
In certain applications, it is desirable to transfer data, commands and power among many modules along a cable which may be hundreds of meters in length. This must be done with low power, with a date rate of, for example, up to 12 megabits per second, and with as low a cost as possible. For example, studying sound propagation in shallow water may require an array of in-line hydrophones, with electronics connected by robust and interchangeable cable sections, which cable sections form a digital bus, controlled at one end by a microprocessor, which in turn is controlled via radio link by a shipboard computer. Through such a system, many array characteristics including gain, bandpass, sampling rate and element acivity are easily changed by the operator. Obviously, in such an application, the cable must be robust to enable the array of hydrophones to be deployed and recovered by letting out and winding in the cable. An ordinary data bus with parallel conductors arranged in a common plane is not useable in such an application. Coaxial cables, twisted wire pairs and optical fibers can be used in conjunction with single conductors but this requires expensive, complicated cables, and usually serialized data paths dedicated to each link. Drive circuits may be complicated and power consuming. Some present systems use analog data transfer, which limits dynamic range and accuracy, and often requires a twisted wire or coaxial cable path for each data link. This leads to large cables for large numbers of modules. One current design uses a coaxial cable with frequency-multiplexed analog data and command transfer. This has a simple cable, but it is analog and has limited controlability and limited data rate.